Feedback vector: ASAN found memory leaks during AST Numbering pass.

Feedback vector: ASAN found memory leaks during AST Numbering pass.

The cause was dynamic allocation of an accounting structure used to
create/initialize the type feedback vector, done at the end of the
numbering pass. The solution is to Zone-allocate the structure to
bring it's lifetime in line with the compilation unit.

BUG=

Review URL: https://codereview.chromium.org/1014793003

Cr-Commit-Position: refs/heads/master@{#27241}